Our objective is to demonstrate the feasibility of an instrument to measure residual urinary bladder volume non-invasively. The instrument is based on ultrasonics, and would specifically be designed for low cost, direct digital readout, and ease of use by relatively untrained personnel. The primary value of the instrument is in reducing the need for catheterization, thus saving patients from the associated discomforts and risks of trauma and infection. Primary applications are: 1. Diagnosis of diseases which involve residual urine problems in the urological office, outpatient clinic, or emergency room; 2. Management of the bladder in spinal cord injury and other neurogenic problems; 3. Determining the need to catherize patients recovering from anesthesia. The product has potential for widespread use by urologists, clinics, and spinal cord care centers. The project includes both the demonstration of technical feasibility, and clinical calibration and evaluation of an experimental instrument. The clinical evaluation phase has several objectives: Test the instrument and processing algorithms for accuracy against catherization derived results. Determine accuracy over enough data points to be significant. Provide data to be used for off-line refinement of the processing. Determine how reliably the instrument can be applied over the range of potential patients, including sex, age, extent of bladder filling, obesity, and extravesical pathology. Investigate clinical value in the following applications: (a) Ambulatory office or clinical diagnosis, (b) Spinal cord injury patient management, (c) Post-anesthetic patient care. Because of the patient benefits and the excellent potential for widespread use, we think the project will be of interest to the National Institute of Arthritis, Diabetes, and Kidney Diseases.